Radiation detection apparatus for changing sensitivity of radiation sensing during control for radiation imaging, method of controlling the same, and non-transitory computer-readable storage medium

ABSTRACT

A radiation detection apparatus detects radiation and generates irradiation sensing information corresponding to a dose of detected radiation, senses whether radiation emitted from a radiation generator is detected, based on the generated irradiation sensing information, and receives a control signal from a controller. The apparatus switches detectability for detection of the radiation based on a control signal received from the controller.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/750,038, filed Jun. 25, 2015, which claims the benefit of andpriority to Japanese Patent Application No. 2014-135167, filed Jun. 30,2014, each of which are hereby incorporated by reference herein in theirentirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a radiation detection technique and,more particularly, to a radiation detection apparatus which can obtainan X-ray image without exchanging any synchronization signal with aradiation generator, a method of controlling the same, and anon-transitory computer-readable storage medium.

Description of the Related Art

Recently, the digitization of radiation images such as X-ray images hasbeen promoted in the medical field, leading to many merits. For example,it is possible to speed up diagnosis by allowing a user to quickly checkobtained images on a display device or the like upon digitaltransmission to it. In addition, digitization improves diagnosisaccuracy with respect to a fine lesion as well as automating diagnosisby various types of image processing. Furthermore, since there is noneed to secure a film storage space, the space efficiency inside ahospital greatly improves. Moreover, since digital transmission hardlysuffers deterioration in data, it is possible to transmit obtainedimages to a remote place without any deterioration. Making the most ofthese features can receive diagnosis from a highly trained doctor bytransmitting images obtained in a home care site, a disaster site, orthe like to a fully-equipped urban hospital.

Radiation imaging apparatuses have been commercially available and arerapidly popular, which use a digital radiography method of forming animage by converting radiation into an electric signal by using aplurality of radiation detecting elements arrayed in a two-dimensionalmatrix instead of a film. As a radiation imaging apparatus of this type,an X-ray detection apparatus using an FPD (Flat Panel Detector) has beenproposed. In such an X-ray detection apparatus, minute X-ray detectors,each obtained by stacking a solid-state photoelectric conversion elementand a scintillator which converts X-rays into visible light, arearranged, as image sensing elements, in a two-dimensional matrix, andeach image sensing element converts irradiated X-rays with which anobject is irradiated into an electric signal (charge amount)corresponding to the dose of irradiation. In general, an FPD canaccumulate the charges, generated by X-ray irradiation, in solid-statephotoelectric conversion elements by controlling a voltage to be appliedto the elements. Thereafter, the FPD reads out charges from thesolid-state photoelectric conversion elements by controlling the voltageto be applied to another voltage, and forms image data in accordancewith the accumulated charge amounts.

When obtaining an X-ray image by using the FPD, it is necessary, inconsideration of the characteristics of the solid-state photoelectricconversion elements in use, to accurately synchronize the timing ofX-ray irradiation with the timing when the detectors accumulate charges(imaging). For this reason, as disclosed in, for example, JapanesePatent No. 4684747, there has been proposed an X-ray imaging systemwhich synchronizes X-ray irradiation with the timing of imaging byexchanging synchronization signals between the X-ray generator and theFPD. More specifically, the FPD makes preparation for imaging inresponse to an irradiation request signal from the X-ray generator, andan irradiation permission signal is transmitted to the X-ray generatorin accordance with the start of imaging by the FPD (the start of theaccumulation of charges), thereby irradiating an object with X-rays. Inthe X-ray imaging system proposed in Japanese Patent Laid-Open No.11-155847, the FPD detects the timing of X-ray irradiation by detectinga change in current caused inside upon X-ray irradiation, and startsimaging in response to the detection as a trigger, thereby establishingsynchronization between X-ray irradiation and the timing of imaging.

In a system in which the X-ray generator and the X-ray detectionapparatus mutually exchange no synchronization signals, the X-raygenerator can generate X-rays regardless of whether the X-ray detectionapparatus is ready for imaging. In this case, X-ray irradiation greatlychanges the state of the X-ray detection apparatus. This influences theimage to be obtained by the next imaging operation unless properprocessing is performed. In order to reduce this influence, the X-raydetection apparatus may always detect the start of X-ray irradiationeven before the completion of preparation for imaging as well as afterthe completion of preparation for imaging.

However, there are increasing cases in which since weak signals arehandled for the detection of the start of X-ray irradiation, when theX-ray detection apparatus is always ready for the detection of X-rays,the apparatus erroneously detects, as imaging, an event which is notimaging because of external electromagnetic ware noise or impact. Thecycle time deteriorates due to a detection error or the operation loadfor the restoration from a detection error increases. This leads todeterioration in the efficiency of imagine. In addition, even if noiseresistance is ensured, the power consumption increases.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is a provided aradiation detection apparatus which comprises a detection unitconfigured to detect radiation and generate irradiation sensinginformation corresponding to a dose of detected radiation, a sensingunit configured to sense whether radiation emitted from a radiationgenerator is detected, based on the irradiation sensing informationgenerated by the detection unit, and a communication unit configured toreceive a control signal from a controller, wherein the sensing unitswitches detectability for detection of the radiation based on a controlsignal received from the controller via the communication unit.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an X-ray imaging system according to thefirst embodiment;

FIG. 2 is an equivalent circuit diagram of an X-ray detector accordingto the first embodiment;

FIG. 3 is a graph schematically showing a change in current informationat the time of X-ray irradiation;

FIG. 4 is a flowchart showing the processing of determining the start ofX-ray irradiation according to the first embodiment;

FIG. 5 is a timing chart for the processing of determining the start ofX-ray irradiation according to the first embodiment;

FIG. 6 is a view schematically showing the sectional structure of aphotoelectric conversion element;

FIGS. 7A to 7D are views showing energy bands in the respectiveoperation modes of a photoelectric conversion element;

FIGS. 8A to 8C are timing charts for overall X-ray examinationprocessing;

FIG. 9 is a timing chart showing the driving timing of an X-raydetector;

FIG. 10 is a graph representing a temporal change in noise in currentinformation;

FIG. 11 is a timing chart for the processing to be performed when X-raysare sensed in sensing mode 3;

FIG. 12 is a flowchart (part 1) showing the processing to be performedwhen X-rays are sensed in sensing mode 3;

FIGS. 13A and 13B are graphs each exemplifying a detection waveform andvibrational noise at the time of imaging; and

FIG. 14 is a flowchart (part 2) showing the processing to be performedwhen X-rays are sensed in sensing mode 3.

DESCRIPTION OF THE EMBODIMENTS

The embodiments of the present invention will be described in detailbelow with reference to the accompanying drawings. Although thefollowing embodiments will exemplify cases in which X-ray images areobtained, the effects of the present invention can also be obtained evenin imaging operations using α-rays, β-rays, and γ-rays as radiationsother than X-rays and other electromagnetic waves.

First Embodiment

FIG. 1 is a block diagram showing the arrangement of an X-ray imagingsystem 10 according to the first embodiment. The X-ray imaging systemaccording to this embodiment includes a power source unit 105, an X-raydetection apparatus 100, an X-ray generator 200, an X-ray controller210, a computer device 400, a display device 410, and a storage device420. The X-ray detection apparatus 100 according to the embodimentincludes an X-ray detector 110 constituted by a two-dimensional imagesensing element 120 and a bias power source 140, an X-ray irradiationsensing unit 150, a control unit 160, a driving unit 165, a readout unit170, an image processing unit 175, an image storage unit 190, and acommunication unit 180.

The X-ray detection apparatus 100 includes an X-ray sensor (radiationsensor) including the two-dimensional image sensing element 120 and ascintillator. The two-dimensional image sensing element 120 is formed byarraying a plurality of solid-state photoelectric conversion elements ina two-dimensional matrix. The bias power source 140 supplies a biasvoltage to the two-dimensional image sensing element 120. The X-rayirradiation sensing unit 150 (sensing circuit) is connected to the biaspower source 140 and senses X-ray irradiation. The control unit 160controls various types of operations of the X-ray detection apparatus100. The readout unit 170 reads out image data. The image processingunit 175 processes the readout image. The communication unit 180 is acommunication circuit having an antenna, and performs reception and thelike of control signals transmitted from the computer device 400 forcontrol located outside. Although the computer device 400 is assumed tobe a general PC (Personal Computer), a smart device or cellular phonemay be used. In some cases, an in-hospital server or cloud system may beused. In addition, in some cases, it is possible to use a systemarrangement obtained by incorporating the X-ray detection apparatus 100with a display in the computer device 400 for control.

The X-ray generator 200 generates pulse-like X-rays 220. The X-raycontroller 210 controls X-ray generation conditions such as an X-rayON/OFF operation, a tube current, and a tube voltage for the X-raygenerator 200. The X-rays 220 generated by the X-ray generator 200irradiate an object 300. The X-rays 220 transmitted through the object300 enter the two-dimensional image sensing element 120 arranged in theX-ray detection apparatus 100. The two-dimensional image sensing element120 converts the X-rays 220 into an X-ray image (radiation image). TheX-ray image is read out by the readout unit 170 (readout circuit) andthen stored in the image storage unit 190 via the image processing unit175. The image storage unit 190 has a storage capacity large enough tostore at least one image data.

The image data completely stored in the image storage unit 190 istransmitted to the outside via the communication unit 180. In this case,while the image data is stored in the image storage unit 190, the imagedata may be simultaneously transmitted to the outside. However, it ispossible to hold all the image data in the image storage unit 190. Thisis because the X-ray detection apparatus 100 can retransmit the imagedata when, for example, part of the image data is not transmittedbecause of a defective communication state or the like, and an externalcomputer device or the like cannot reproduce an accurate image. Theimage transmitted to the outside is stored in the storage device 420 ordisplayed on the display device 410. The communication unit 180 may haveeither a wired communication function or a wireless communicationfunction. In addition, image data may be stored in the storage device420 without via the computer device 400. Alternatively, the X-raydetection apparatus 100 may incorporate a storage unit (not shown) otherthan the image storage unit 190 and can store image data in the storageunit.

In addition, the power source unit 105 is connected to the X-raydetection apparatus 100. If the communication unit 180 has the wirelesscommunication function, the X-ray detection apparatus 100 generallyincorporates a battery as the power source unit 105. If thecommunication unit 180 has the wired communication function, a powersource capable of wired connection is connected as the power source unit105 to the X-ray detection apparatus 100 according to one embodiment.Note that when the communication unit 180 has the wired communicationfunction, the X-ray detection apparatus is often used while beingmounted on a standing gantry or embedded in a table according to oneembodiment. The communication unit 180 sometimes has both the wirelesscommunication function and the wired communication function. In thiscase, the wired communication function and the wireless communicationfunction of the communication unit 180 are automatically switched uponbeing attached/detached to/from a cradle or the like, and the powersource unit 105 is switched accordingly between a built-in battery and awired power source.

FIG. 2 is an equivalent circuit diagram of the X-ray detector 110. Thetwo-dimensional image sensing element 120 is constituted by a pluralityof pixels arrayed in an m (row) x n (column) matrix. For the sake ofdescriptive simplicity, FIG. 2 shows a 3×3 matrix, with m=3 and n=3.However, an actual detection apparatus includes many pixels, forexample, m=2800 and n=2800. Each pixel, as exemplified as a pixel 125,is constituted by a photoelectric conversion element S11, a phosphor(not shown) which converts the X-rays 220 into light in a wavelengthband that can be sensed by the photoelectric conversion element S11, anda switch element T11.

Each photoelectric conversion element (S11 to S33) generates andaccumulates charges corresponding to the incident dose of X-rays. Thetransmission dose of X-rays through the object 300 differs indistribution depending on through which part in the object, includingstructures such as bones and internal organs and focuses of disease,X-rays are transmitted. Each photoelectric conversion element (S11 toS33) converts such a distribution, which differs in this manner, intothe distribution of charges and accumulates it. As each photoelectricconversion element (S11 to S33), various types of elements usingamorphous silicon and polysilicon are known, as well as a CCD. In thisembodiment, as each photoelectric conversion element (S11 to S33), a MISphotodiode made of amorphous silicon as a main material and arranged onan insulating substrate such as a glass substrate is used. However, aPIN photodiode may be used. In addition, a direct type conversionelement which directly converts radiation into charges can be suitablyused. As each switch element (T11 to T33), a transistor having a controlterminal and two main terminals is suitably used. This embodiment uses aTFT (Thin-Film Transistor).

In the pixel 125, the electrode on the lower electrode side is shown asthe G electrode, and the electrode on the upper electrode side is shownas the D electrode. In the pixel 125, the D electrode is electricallyconnected to one of the two main terminals of the switch element. On theother hand, the G electrode is connected to the bias power source 140via a common bias wiring. When taking the first row as an example, thecontrol terminals of the plurality of switch elements T11, T12, and T13in the row direction are commonly connected to a driving wiring g1 onthe first row, and the driving unit 165 (driving circuit) supplies adriving signal for controlling the conductive states of the switchelements T11, T12, and T13 via the driving wiring g1 for each row.

When taking the first column as an example, the main terminals of theplurality of switch elements T11, T21, and T31 in the column direction,which are not connected to the photoelectric conversion elements S11,S21, and S31, are electrically connected to a signal wiring s1 on thefirst column. While the switch elements T11, T21, and T31 are in theconductive state, electric signals corresponding to the charge amountsaccumulated in the photoelectric conversion elements S11, S21, and S31are output to the readout unit 170 via the signal wiring s1. A pluralityof signal wirings s1 to s3 in the column direction parallelly transmitthe electric signals read out from a plurality of pixels to the readoutunit 170.

The readout unit 170 includes a multiplexer (not shown) whichsequentially processes parallelly readout electric signals and outputsthe resultant signals as a serial image signal and a buffer amplifier(not shown) which outputs the image signal after impedance conversion.An AD converter 171 converts the image signal as the analog electricsignal output from the buffer amplifier into digital image data.

The bias power source 140 supplies a bias voltage Vb to the G electrodeof each photoelectric conversion element (S11 to S33) via the biaswiring, and also outputs current information containing a change incurrent amount supplied to the bias wiring. In this embodiment, acircuit (sensing circuit) which outputs current information for sensingX-ray irradiation includes a current-voltage conversion circuit 141constituted by an operational amplifier and a resistor and an ADconverter 142 which converts a converted output voltage into a digitalvalue. However, this is not exhaustive. For example, a current-voltageconversion circuit using a shunt resistor may be used. In addition, thebias power source 140 may directly output an output voltage from thecurrent-voltage conversion circuit 141. Furthermore, the bias powersource 140 may output a physical amount corresponding to the currentamount supplied to the bias wiring.

The current information output from the bias power source 140 is sent tothe X-ray irradiation sensing unit 150. This information is used tosense X-ray irradiation by capturing a change in current amount causedduring X-ray irradiation. In addition, the bias power source 140 alsoincludes a refresh voltage Vr. Like a voltage Vs, the voltage Vr isconnected to the G electrode of each photoelectric conversion element(S11 to S33) via the bias wiring. The voltage Vr is applied to the Gelectrode during a refresh period of the photoelectric conversionelement. An SW control circuit 143 controls a voltage to be applied tothe G electrode. The SW control circuit 143 performs control to applythe voltage Vr during a refresh period (refresh mode period) and thevoltage Vs during a period (photoelectric conversion mode period) otherthan the refresh period.

A method of sensing X-ray irradiation according to this embodiment willbe described below. As information for sensing X-ray irradiation, thecurrent information on the bias wiring described above can be usedwithout any change. The X-ray irradiation sensing unit 150 can determinethe start of X-ray irradiation by determining whether a sampled value ofan input current exceeds a predetermined threshold. Setting a lowthreshold allows the X-ray irradiation sensing unit 150 to quickly sensethe start of X-ray irradiation. In this case, however, the X-rayirradiation sensing unit 150 becomes susceptible to, for example, animpact or magnetic field noise and may suffer erroneous sensing (a statein which it determines the occurrence of irradiation in spite of thefact that no X-ray irradiation has occurred). In contrast to this,setting a high threshold will decrease the risk of erroneous sensingcaused by noise in the X-ray irradiation sensing unit 150. However, thiswill delay the timing of sensing X-ray irradiation. Prolonging the timefrom the start of X-ray irradiation to the sensing of it will cause anartifact in an image. In consideration of this problem, the time fromthe start of irradiation to the determination of it can be shorter. Itis possible to decide an optimal sensing threshold in consideration ofthese points.

In addition, the X-ray sensing sensitivity may be decreased by adjustingthe bias voltage Vb to be applied (for example, setting a low bias atthe time of accumulation by setting the voltage Vs to a high voltage)when detecting X-rays with low sensitivity. In this case, the standbytime shortens to produce merits, such as reducing the load on each X-raydetecting element and shortening the recovery time from refresh.However, using the current information without any change will arise aproblem that the sensing performance changes in accordance with theincident dose of X-rays per unit time.

FIG. 3 is a graph schematically showing the current information (biascurrent) output from the bias power source 140 upon X-ray irradiation.FIG. 3 shows the state of the second X-ray irradiation. Areas A and Brespectively defined by the products of the irradiation time widths andthe values of the bias currents in the first irradiation and the secondirradiation are equal to each other, and hence there is no densitydifference between obtained images. That is, identical images can beobtained by the first irradiation and the second irradiation. On theother hand, the X-ray irradiation time in the first irradiation isshorter than that in the second irradiation. This is equivalent to thatX-rays are output with a higher tube current in the first irradiation(assume that other imaging conditions such as a tube voltage, an objectand a distance between a tube and FPD remain the same). Checking achange in bias current at this time reveals that the crest value (thevalue of the bias current) in the first irradiation is higher than thatin the second irradiation. If, therefore, a threshold is set asindicated by the dotted line in FIG. 3, it can occur that the firstirradiation is sensed because the crest value is higher than thethreshold, but the second irradiation is not be sensed because the crestvalue is lower than the threshold. Some X-ray generator cannot generatea high tube current. A combination with such an X-ray generator may leadto the risk of failing to sense irradiation.

In order to cope with such a problem, in this embodiment, the X-rayirradiation sensing unit 150 determines whether X-ray irradiation isstarted, by integrating values X[N] obtained by sampling currentinformation on a bias wiring. FIG. 4 is a flowchart for thedetermination of the start of X-ray irradiation. FIG. 5 is a timingchart for the determination of the start of X-ray irradiation. First ofall, the X-ray irradiation sensing unit 150 respectively gives theinitial values to Sum representing an integral value, n representing theindex of a sampled value, and m representing an integral interval number(step S401). The initial values are respectively Sum=0, n=0, and m=1.This operation will be called integrator resetting. The X-rayirradiation sensing unit 150 then sets, as the new integral value Sum,the value obtained by adding the integral value sum and X[n]representing a sampled value preceding by n values. That is,Sum=Sum+X[n] (step S402). After such cumulative addition, the X-rayirradiation sensing unit 150 sets n=n+1 (step S403), and then performsinterval determination (step S404).

In the interval determination in step S404, if the index n of a sampledvalue does not exceed a pre-designated mth integral interval W[m] (NO instep S404), the X-ray irradiation sensing unit 150 performs cumulativeaddition again. If the index n of the sampled value exceeds W[m] (YES instep S404), the X-ray irradiation sensing unit 150 performs sensingdetermination (step S405). In the sensing determination in step S405, ifthe integral value Sum exceeds a pre-designated threshold T[m] in themth interval (YES in step S405), the X-ray irradiation sensing unit 150outputs information indicating the start of X-ray irradiation (stepS408). If the integral value Sum does not exceed the threshold T[m] inthe mth interval (NO in step S405), the X-ray irradiation sensing unit150 sets m=m+1 (step S406), and performs end determination (step S407).In the end determination in step S407, if the integral interval number mdoes not exceed the number M of integral intervals (NO in step S407),the X-ray irradiation sensing unit 150 performs cumulative additionagain. If m exceeds M (YES in step S407), the X-ray irradiation sensingunit 150 outputs X-ray information indicating that X-ray irradiation isnot started (step S409).

In general, M is a value equal to or more than 1. The larger the valueM, the wider the range of irradiation conditions which can be detected.Shortening the integral interval will widen a range corresponding toimaging conditions for a short irradiation time with a high output. Incontrast to this, prolonging the integral interval will widen a rangecorresponding to imaging conditions for a long irradiation time with alow output. Since adaptive irradiation conditions differ depending onintegral interval settings, the X-ray irradiation sensing unit 150 canadapt to almost all the necessary irradiation conditions by setting aplurality of integral intervals at proper intervals.

In addition, the threshold T[m] in each integral interval may be keptconstant regardless of the integral interval number m or may be set toan optimal value for each integral interval. In general, it is possibleto set optimal thresholds in accordance with the amounts of noisecontained in current signals differing for the respective integralintervals. For example, it is possible to measure the standard deviationof noise amounts and set, as a threshold, a value of an integralmultiple of the measured standard deviation.

For example, an operation to be performed when the integral intervalnumber M is 4, first integral interval W[1]=8, second integral intervalW[2]=16, third integral interval W[3]=32, and fourth integral intervalW[4]=64 will be described in detail below as an example. First of all,the X-ray irradiation sensing unit 150 respectively gives the initialvalues to Sum representing an integral value, n representing the indexof a sampled value, and m representing an integral interval number (stepS401). The initial values are Sum=0, n=0, and m=1. The X-ray irradiationsensing unit 150 then sets, as the new integral value Sum, the valueobtained by adding the integral value sum and X[0] representing asampled value preceding by 0 value (step S402). That is, Sum=Sum+X[0].After such cumulative addition, the X-ray irradiation sensing unit 150sets the index of the sampled value to n=n+1 (step S403), and thenperforms interval determination (step S404). After the first cumulativeaddition, the index of the sampled value is n=1, and hence does notexceed first integral interval W[1]=8. That is, since NO in the intervaldetermination, the X-ray irradiation sensing unit 150 performscumulative addition again (NO in step S404→step S402).

After such cumulative addition is repeated eight times, the valueobtained by integrating eight sampled values is stored in the integralvalue Sum. In addition, the index of the sampled value is n=8, and henceexceeds first integral interval W[1]=8. That is, since YES is obtainedin the interval determination in step S404, the X-ray irradiationsensing unit 150 performs sensing determination (step S405). In thesensing determination, if the integral value Sum does not exceed apre-designated threshold T[1] in the first interval, the X-rayirradiation sensing unit 150 sets the integral interval number to m=m+1(step S406), and then performs end determination (step S407). After thefirst sensing detection, the integral interval number is m=1, and hencedoes not exceeds M=4, which represents the number of integral intervals.That is, since NO is obtained in the end determination in step S407, theX-ray irradiation sensing unit 150 performs cumulative addition again(step S402). When the X-ray irradiation sensing unit 150 repeatscumulative addition 64 times while the threshold T[m] is not exceeded ineither integral interval, the integral interval number becomes m=4. As aconsequence, YES is obtained in the end determination (YES in stepS407). At this time, the X-ray irradiation sensing unit 150 outputsX-ray information indicating that X-ray irradiation is not started (stepS409). In contrast to this, if the threshold T[m] is exceeded in thesensing determination, the X-ray irradiation sensing unit 150 outputsX-ray information indicating the start of X-ray irradiation at this timepoint.

The above description has exemplified the arrangement in which the X-raydetection apparatus 100 performs sensing determination in a plurality ofintegral intervals by using one integrator. However, M integrators maybe prepared in correspondence with M integral intervals in the X-raydetection apparatus 100 to parallelly perform sensing determination byusing the respective integrators. In addition, the above description hasexemplified the arrangement in which the X-ray irradiation sensing unit150 senses the start of X-ray irradiation when the threshold is exceededin any one of the integral intervals. However, the X-ray irradiationsensing unit 150 may determine the start of X-ray irradiation when thethreshold is exceeded in a plurality of integral intervals.

The operations of photoelectric conversion elements (for example, S11 toS33 in FIG. 2) will be described next. As described above, the operationmodes of each photoelectric conversion element according to thisembodiment include the two types, namely, the refresh mode and thephotoelectric conversion mode. FIG. 6 is a view schematically showing asection of each photoelectric conversion element according to thisembodiment. Various types of materials are deposited and stacked on aglass substrate 130 formed from an insulating substrate to form aphotoelectric conversion element. An upper electrode 135 is formed froma transparent electrode. A lower electrode 131 is formed from Al, Cr, orthe like. An insulating layer 132 is formed from an amorphous siliconnitride film to inhibit both electrons and holes. An intrinsicsemiconductor layer 133 is formed from hydrogenated amorphous silicon,which generates electron-hole pairs when light enters, and operates as aphotoelectric conversion layer. An impurity semiconductor layer 134 isformed from n-type amorphous silicon and operates as a hole blockinglayer which blocks the injection of holes from the upper electrode 135into the intrinsic semiconductor layer 133.

FIGS. 7A to 7D are energy band diagrams of each photoelectric conversionelement. FIG. 7A shows a state without any bias. FIG. 7B shows a statein the photoelectric conversion mode. FIG. 7D shows a state in therefresh mode. In the photoelectric conversion mode in FIG. 7B, thevoltage Vs as a bias voltage is applied between the upper electrode 135and the lower electrode 131 such that a positive voltage appears on theupper electrode 135. The voltage Vs sweeps out electrons in theintrinsic semiconductor layer 133 from the upper electrode 135. On theother hand, holes are tried to be injected from the upper electrode 135to the intrinsic semiconductor layer 133 but are blocked by the impuritysemiconductor layer 134 and cannot move to the intrinsic semiconductorlayer 133.

When light enters the intrinsic semiconductor layer 133 in this state,electron-hole pairs are generated by a photoelectric conversion effect.The electrons and holes move in the intrinsic semiconductor layer 133without recombining in accordance with an electric field. The electronsare swept out from the upper electrode 135, but the holes are blocked bythe insulating layer 132 and stay on its interface. When thephotoelectric conversion operation continues and holes staying on theinterface of the insulating layer 132 increase in number, the electricfield applied to the intrinsic semiconductor layer 133 is weakened bythe influence of the holes. As a result, the electron-hole pairsgenerated by the incident light disappear by recombination withoutmoving by the electric field, and the photoelectric conversion elementloses sensitivity to light. FIG. 7C is an energy band diagram at thistime. Such a state is called saturation.

In order to make a saturated photoelectric conversion element recoversensitivity, the photoelectric conversion element needs to perform anoperation called refresh. In the refresh mode of performing a refreshoperation, as shown in FIG. 7D, the voltage Vr is applied between theupper electrode 135 and the lower electrode 131 such that a positivevoltage appears on the lower electrode 131. In the refresh mode, holesstaying on the interface of the insulating layer 132 are swept out fromthe upper electrode 135, and electrons are injected instead of the holesand stay on the interface of the insulating layer 132. In this case,when the photoelectric conversion element is switched again to thephotoelectric conversion mode (FIG. 7B), the injected electrons arequickly swept out from the upper electrode 135, and the voltage Vs isapplied as a bias voltage to make the photoelectric conversion elementrecover sensitivity to light.

As described above, each photoelectric conversion element needs toperiodically operate in the refresh mode to maintain sensitivity tolight. First of all, refresh is required immediately after light enters.This timing corresponds to a timing immediately after X-ray irradiation.That is, when an X-ray image is obtained by X-ray irradiation, eachphotoelectric conversion element needs to operate in the refresh modefor preparation for the next imaging operation to recover sensitivity.Even in a state without any irradiation, charges (dark current) arerandomly generated in each photoelectric conversion element owing to theinfluences of a temperature and the like. The accumulation of chargesgenerated randomly in this manner also makes each photoelectricconversion element gradually lose sensitivity. For this reason, when astate without irradiation continues for a predetermined time or more,each photoelectric conversion element needs to be refreshed.

Note that when a PIN photodiode or the like is used as thetwo-dimensional image sensing element 120, the above refresh mode itselfis not required. However, an imaging recovery time shortening mode to beexecuted upon some kind of change in driving has a significance similarto that of the use of the refresh mode in this embodiment. Changes indriving include, for example, a change in bias including temporary biasstoppage with respect to the normal mode, a change in driving timing,and a reset operation by another light-emitting device.

The relationship between each X-ray sensing mode of the X-ray detectionapparatus and an X-ray examination state will be described next. FIGS.8A to 8C are timing charts representing the relationships between theX-ray sensing modes and overall X-ray examination operations. FIGS. 8Ato 8C show cases in which the X-ray detection apparatus 100 sensesX-rays in three sensing modes. The first is sensing mode 1 correspondingto a preparation period from the end of imaging by the X-ray detectionapparatus 100 to the completion of preparation for imaging. The secondis sending mode 2 corresponding to an irradiation determination periodfrom the completion of preparation for imaging to the detection of X-rayirradiation. The third is sensing mode 3 corresponding to a preparatoryirradiation determination period with low possibility of X-rayirradiation after mode switching immediately after activation or insynchronism with a change in irradiation determination criterion as atrigger. The function associated with X-ray detection can be keepeffective, from the viewpoint of reducing ineffective exposure. For thisreason, the X-ray detection apparatus 100 detects X-rays even in aperiod, as a preparatory irradiation determination period, in which thepossibility of X-ray irradiation is low, from the contents ofinstructions from the operator or information acquired by the X-raydetection apparatus 100.

In this embodiment, different thresholds for X-ray sensing arerespectively set in sensing mode 1, sensing mode 2, and sensing mode 3.Letting T1 be the threshold in sensing mode 1, T2 be the threshold insensing mode 2, and T3 be the threshold in sensing mode 3, T3>T1>T2.That is, the highest X-ray detectability is set in the period of sensingmode 2, and the lowest X-ray detectability is set in the period ofsensing mode 3. Sensing mode 1 is a mode corresponding to a preparatoryperiod in which current information is unstable. In this mode, a highthreshold is set to prevent erroneous sensing caused by noise and thelike. As described above, sensing mode 3 is a mode corresponding to aperiod with low possibility of irradiation, and hence a high thresholdis set in this mode as in sensing mode 1 to prevent erroneous sensingcaused by noise and the like. Note that if it is obvious that no X-rayirradiation is performed in the period of sensing mode 3, T3 may be setto infinity, that is, setting not to perform X-ray detection. Inaddition, the state of sensing mode 2 may be called the ON state of thefunction of sensing the start of irradiation, and the states of theremaining modes may be called the OFF state of the function of sensingthe start of irradiation.

As shown in FIG. 8A, upon confirming that the power source is turned on,the X-ray detection apparatus 100 performs an initializing operationfirst. During this initialization, the sensing mode of X-ray irradiationdetermination is in a non-sensing state. Upon completion of theinitializing operation, the sensing mode shifts to sensing mode 3(preparatory irradiation determination period). Different conditions areset for the shift from the state after the activation to sensing mode 3depending on the power source state for the X-ray detection apparatus100. If, for example, the X-ray detection apparatus 100 is incorporatedin a standing gantry or imaging table and always receives power from thepower source unit 105, the state after the activation shifts to sensingmode 3 as soon as the completion of initialization. If the X-raydetection apparatus 100 uses an internal power source such as a battery,the state after the activation does not shift to sensing mode 3 untilthe reception of an explicit instruction from the operator or does notshift to sensing mode 3 at the time of the activation. Assume that theX-ray detection apparatus 100 operates on a built-in battery and isinstalled on the condition that no imaging is executed when it isattached to a cradle. In this case, when the X-ray detection apparatus100 is attached to the cradle, the apparatus may stand by in anon-sensing mode, and may shift to sensing mode 3 upon detectingactivity to detach the apparatus from the cradle or a vibration orimpact.

When the operator inputs imaging preparation information to the computerdevice 400, the X-ray detection apparatus 100 receives and checks adetection preparation start command, and then immediately shifts fromsensing mode 3 (preparatory irradiation determination period) to sensingmode 2 (irradiation determination period) through sensing mode 1(preparation period). Note that when the X-ray detection apparatus 100is not in a standby state in sensing mode 3 and receives a detectionpreparation start command in a non-sensing state, the apparatus shiftsto sensing mode 2 after staying in sensing mode 1, for example, for afew seconds. This is because a driving state in the X-ray detectionapparatus 100 in sensing mode 3 is almost the same as that in sensingmode 1, and a predetermined preparation period is required to read outan X-ray image. Note that when performing the first imaging operationupon activation of the power source, the X-ray detection apparatus 100may shift to sensing mode 2 without being through sensing mode 1, asshown in FIG. 8A.

Upon detecting X-ray irradiation during the period of sensing mode 2,the X-ray detection apparatus 100 reads out an image and transfers it.In this period, the apparatus is set in a non-sensing state. Uponchecking a detection preparation start command after performing arefresh operation, the X-ray detection apparatus 100 shifts to sensingmode 1, and then shifts to sensing mode 2 upon checking an imagingpermission command.

FIG. 8B shows a case in which the X-ray detection apparatus 100 shiftsto sensing mode 3 (preparatory irradiation determination period) afterthe end of imaging of patient A (sensing mode 1). Upon completion of thesecond imaging operation for this specific object (patient A), the X-raydetection apparatus 100 notifies the computer device 400 of thecompletion of detection preparation, and then waits for a radiationimaging permission command from the computer device 400. Assume that theX-ray detection apparatus 100 cannot confirm the reception of aradiation imaging permission command as an instruction signal within apredetermined period (timeout time A) after notification of thecompletion of detection preparation. In this case, the X-ray detectionapparatus 100 regards that the operator has no intention to performimaging, and then shifts to sensing mode 3 (OFF state).

In addition, as shown in FIG. 8C, upon receiving an imaging end commandfrom the computer device 400, the X-ray detection apparatus 100 mayshift to sensing mode 3 (OFF state). This imaging end command is issuedwhen an operation input is performed to instruct the end of examinationof a specific object. Upon shifting to sensing mode 3, the X-raydetection apparatus 100 operating on a built-in battery may shift fromsensing mode 3 to a non-sensing state when a predetermined time (timeouttime B: for example, 10 min) has elapsed after the end of the previousimaging operation to save the battery duration. In contrast to this, ifthere is no need to consider the battery duration or durability, theX-ray detection apparatus 100 may continue sensing mode 3. In addition,the X-ray detection apparatus 100 may return from a non-sensing state atthe timing of being detached from the cradle or sensing a vibration orthe like as shown in FIG. 8C as well as receiving an explicit commandfrom the computer device 400. This is because the X-ray detectionapparatus 100 regards that such an operation or the like at this timingmay be one of a series of operations for imaging preparation.

FIG. 9 is a timing chart showing the driving timing of the X-raydetector 110 and indicating an operation from some midpoint inirradiation sensing driving (initial reading driving). A preparationperiod will be described in detail below with reference to FIG. 9.Initial reading driving is a driving operation to sequentially turn onthe switch elements of the photoelectric conversion elements from thestart row (y=0) to the last row (y=m), and is performed to removecharges originating from dark currents generated in the photoelectricconversion elements. Initial reading driving is repeated in apredetermined cycle until X-ray irradiation is sensed. In this period,the bias voltage Vb is always kept at the voltage Vs.

Upon X-ray irradiation, the charge amount read out by initial readingincreases. At this time, the current flowing in the bias line alsoincreases. The current information of the bias current is input to theX-ray irradiation sensing unit 150, and the start of X-ray irradiationis sensed. In this case, every time initial reading from one row isperformed, integration is performed to add a sampled value X[n], and theresultant value is compared with a predetermined threshold to determinethe start of irradiation. When the start of X-ray irradiation isdetermined, the initial reading driving is stopped at this time point(the start of X-ray irradiation is sensed on the ith row in FIG. 9), theoperation shifts to the operation of accumulating charges. During theaccumulation of charges, all the switch elements are OFF. When theaccumulation is finished after the lapse of a predetermined time, theoperation shifts to actual reading. Actual reading is performed bysequentially turning on the switch elements from the start row (y=0) tothe last row (y=m).

After actual reading, refresh is immediately performed. Refresh isperformed by setting the bias voltage Vb to the voltage Vr. At thistime, the X-ray detector 110 may execute refresh simultaneously withrespect to all the lines or sequentially. Alternatively, the X-raydetector 110 may divide the lines into several blocks and executerefresh for each block. After the refresh is finished, initial readingis started again.

During the accumulation of charges, actual reading, and refreshoperation, no current signal used by the X-ray irradiation sensing unit150 can be obtained, and hence X-ray irradiation cannot be sensed.Therefore, the X-ray irradiation sensing unit 150 is OFF. In addition,since a current signal is unstable immediately after the refresh mode isswitched to the photoelectric conversion mode, the accuracy of sensingX-ray irradiation deteriorates until a current signal becomes stable.For this reason, the X-ray irradiation sensing unit 150 sometimeserroneously senses that X-ray irradiation has been performed, that is,“erroneous sensing” sometimes occurs, in spite of the fact that no X-rayirradiation has been performed. It is therefore necessary to keep theX-ray irradiation sensing unit 150 OFF for a predetermined period. If,however, X-ray irradiation is erroneously performed during a period inwhich the X-ray irradiation sensing unit 150 is OFF, no irradiationsensing is performed. This may cause unnecessary exposure of a patientas an object. In addition, the following problems arise.

First of all, along with irradiation, charges are generated in eachphotoelectric conversion element as in a normal operation. Although thegenerated charges are gradually removed by initial reading, chargeswhich cannot be removed are accumulated. If imaging is performed in thisstate after a preparation period, the residual components of the chargesgenerated by erroneous irradiation are superimposed on the chargesgenerated by the imaging operation, resulting in a deterioration in theimage quality of an obtained image. In addition, assume that apreparation period ends immediately after erroneous irradiation, andsensing is started. In this case, since a large amount of chargesgenerated by erroneous irradiation stay, many charges are read out byinitial reading immediately after the start of the operation of theX-ray irradiation sensing unit 150. This may make the X-ray irradiationsensing unit 150 output an image upon erroneously sensing irradiation.In this case, since imaging has not been actually performed, the imagequality of the obtained image does not reach a predetermined level. Itis therefore highly possible that the image cannot be properly used fordiagnosis or the like. The imaging technician needs to perform, forexample, misshooting processing for such images. This can increase theload on the technician.

In addition, owing to the charges generated by erroneous irradiation,the photoelectric conversion element is forced into a state like thatshown in FIG. 7C. As a result, the sensitivity of the pixel itself tolight deteriorates, the saturation level to incident light decreases,and the dynamic range of the image narrows. This leads to a considerabledeterioration in image quality. At the same time, the sensitivity of theX-ray irradiation sensing unit 150 itself deteriorates, and hence it isnot possible to accurately sense normal irradiation. This may cause thepatient to repeatedly undergo ineffective exposure.

In order to minimize ineffective exposure of a patient, the X-raydetection apparatus 100 needs to sense exposure during an erroneousperiod and refresh each photoelectric conversion element. For thispurpose, it is possible to minimize a preparation period and sense X-rayirradiation over a long period. In this embodiment, the X-ray detectionapparatus 100 has a plurality of sensing modes, and uses differentsensing modes in a preparation period and a sensing period, therebysensing irradiation immediately after refresh driving.

In addition, even after the end of imaging of one patient, the X-raydetection apparatus 100 can always continue the X-ray sensing functionfrom the viewpoint of reducing X-ray exposure as described above. On theother hand, to always continue the X-ray sensing function is to stand bywhile keeping the X-ray sensing function effective during a period fromthe end of imaging of one patient to the start of preparation forimaging of the next patient, in spite of the fact that the probabilityof X-ray irradiation is not high in the period. If X-ray irradiation iserroneously detected in such a period, it is necessary to perform, forexample, misshooting processing. This may increase the load on theimaging technician. In such a period, therefore, it is effective tochange an X-ray detection state based on a signal explicitly indicatingan intention not to perform imaging in accordance with an instruction oroperation from the operator while making the X-ray detection apparatus100 continue X-ray detection.

In this case, a preparation period (a period corresponding to sensingmode 1) is a period in which a current signal for X-ray irradiationsensing after refresh and an offset component are unstable. Therefore,similar settings may be made immediately after the activation of theX-ray detection apparatus 100 as well as immediately after refreshdriving. The X-ray detection apparatus 100 may arbitrarily set thelength of a preparation period within a range in which image quality andthe like are guaranteed, and sets the length to, for example, 10 sec.The length of a preparation period may be the same immediately afteractivation and immediately after refresh driving or may be individuallyset. In addition, the X-ray detection apparatus 100 can automaticallyswitch to a period, as a preparation period, in which currentinformation becomes sufficiently stable, in accordance with the state ofthe current information by, for example, monitoring the state of thecurrent information using the X-ray irradiation sensing unit 150. Inthis case, the necessary degree of stability of current information maybe arbitrarily set in consideration of image quality and the like.

FIG. 10 is a graph representing a temporal change in noise amountcontained in current information. On this graph, the value of thestandard deviation (σ) of noise in current information at each timepoint is plotted along the time axis with reference to the timing ofrefresh driving. Referring to FIG. 10, obviously, the noise amountrapidly decreases immediately after the refresh driving, and becomesalmost stable after the lapse of a predetermined time (5 sec in FIG.10). In this case, for example, sensing mode 1 is set in an intervalfrom 3.3 sec to 10 sec, in which the rapid change in noise has becomestable to some extent. A threshold T1 in sensing mode 1 can be set to aconstant multiple of noise (σ) so as to suppress probabilistic erroneoussensing caused by a variation in noise. For example, T1=17 is set as athreshold five times a threshold five times σ (3.4) at 3.3 sec. On theother hand, sensing mode 2 is started after the lapse of 10 sec, and T2is set to 3.26×5=15.3.

When X-ray irradiation is sensed, image accumulation is performedregardless of the sensing mode. Upon completion of image readoutoperation, each element is subjected to refresh driving. The internalstate of each detecting element is reset by the refresh driving to alloweach element to exhibit desired performance at the time of the nextimaging operation. The readout image is processed and stored in theimage storage unit 190.

Note that the image obtained when X-rays are sensed in sensing mode 1has undergone an imaging operation while an offset component isunstable, and hence may not have reached a desired image quality level.Using such an image for diagnosis may lead to a diagnostic error oroversight of a lesion. It is therefore necessary to carefully handlesuch an image. In addition, in sensing mode 1, since the preparation onthe computer device 400 side is not made, information to be linked to anobtained image is unstable. In this case, the information to be linkedto the obtained image includes information for identifying a patient,information concerning an imaging region and an imaging technique, andimaging execution information such as a tube voltage and a tube current.Lacking in such information to be managed upon being linked to an imagemay lead to the confusion of patient information.

A case in which the X-ray detection apparatus 100 has sensed X-rayirradiation in sensing mode 3 (preparatory irradiation determinationperiod) will be described next. FIG. 11 is a timing chart for theprocessing to be performed when X-ray irradiation is sensed in sendingmode 3 according to this embodiment. FIG. 12 is a flowchart for theprocessing. Referring to FIG. 11, the X-ray detection apparatus 100stands by in sensing mode 3 after an initializing operation upon theactivation of the power source. In this case, upon detection of X-rays(imaging of a patient X in FIG. 11), the X-ray detection apparatus 100performs image accumulation and a readout operation as described above(step S1201). Thereafter, the X-ray detection apparatus 100 temporarilystores the obtained image in the image storage unit 190 (step S1202),and determines whether the current imaging operation is actual X-rayimaging or corresponds to external magnetic field noise orvibration/impact noise (step S1203).

FIG. 13A shows an example of a detection waveform at the time of X-rayimaging. FIG. 13B shows an example of vibration noise. When vibrationnoise or external magnetic field noise is detected, a vibrationaldetection waveform like that shown in FIG. 13B is obtained. Therefore,the average value of such a waveform is often near to the pixel value“0”, and often takes a negative value. For this reason, the imagestorage unit 190 handles readout data as a signed image and performsintegration. If the integral value does not exceed a predeterminedthreshold, the image storage unit 190 determines false detection (NO instep S1203). If the integral value exceeds the threshold, the imagestorage unit 190 determines that the data is an X-ray image or highlylikely to be the one (YES in step S1203). In this case, upon waiting forthe completion of preparation for the computer device 400 (step S1204),the communication unit 180 transfers the image (step S1205). In thiscase, the display device 410 can actively display a message to allow thecomputer device 400 to select between storing the image in the storagedevice 420 upon linking it to information such as patient informationand performing misshooting processing (step S1206).

If a detection error is determined (NO in step S1203), the displaydevice 410 does not actively display any message to the user. The X-raydetection apparatus 100 then performs refresh and preparatory driving,and stands by in sensing mode 2→sensing mode 3 to prepare for thepossibility of the next imaging operation. If the operator performs anexplicit image obtaining operation (step S1207), the communication unit180 transfers the image which has already been obtained by the X-raydetection apparatus 100 to the computer device 400 (step S1208). Thecomputer device 400 can select between storing the image in the storagedevice 420 upon linking it to information such as patient informationand performing misshooting processing based on an operation by the user(step S1209).

The computer device 400 may determine whether the X-ray detectionapparatus 100 is ready for imaging (preparation completion state) inaccordance with a communication state with the X-ray detection apparatus100, or may switch between determining that the X-ray detectionapparatus 100 is ready for imaging and determining that the X-raydetection apparatus 100 is not ready for imaging, depending on whetherthe user or the like has performed some kind of operation. In any case,assume that a state in which an image can be safely received immediatelyafter imaging is an imaging ready state, and the period of an imagingready state is regarded as an imaging ready period. In contrast to this,a period in which safe imaging cannot be performed is regarded as animaging inhibition state, and the period of this state is regarded as animaging inhibition period.

When the computer device 400 becomes ready for imaging, the computerdevice 400 notifies the X-ray detection apparatus 100 of thecorresponding information. In response to this operation, theinformation stored in the image storage unit 190 is transferred to thecomputer device 400 via the communication unit 180. The computer device400 has already received patient information to be linked to an image tobe obtained next and other information, and stores the transferred imageupon linking it to these pieces of information. The display device 410displays the transferred image. If the image quality of the image isinsufficient for diagnosis, the computer device 400 may discard theimage by misshooting processing or the like and maintain a state inwhich imaging can be performed again under the same conditions.

In this case, the X-ray detection apparatus 100 may attach, to at leastthe image obtained by sensing X-ray irradiation in sensing mode 1,information indicating that the image has undergone irradiation duringan improper period. In addition, the X-ray detection apparatus 100 maywrite this information in the image data as its header or store theinformation in a file other than the image data. Upon receiving imageinformation attached with such information, the display device 410 maydisplay a dialog indicating that the image has been obtained at animproper irradiation timing, together with the image, to warn theimaging technician. In addition, it is possible to make the technicianto determine whether the image information is necessary, for example, todetermine whether to perform misshooting processing. With theseoperations, the X-ray detection apparatus 100 can obtain even an X-rayimage having undergone irradiation during a preparation period, and thecomputer device 400 can manage the image upon linking it to properinformation.

As described above, according to this embodiment, the radiationdetection apparatus has a plurality of sensing modes, and can performirradiation sensing immediately after refresh driving while avoidingimproper exposure by the radiation generator by setting differentsensing modes in a preparation period and a sensing period,respectively. In addition, performing re-imaging processing and transferprocessing as needed can store information associated with an obtainedimage upon linking the information to the image.

Second Embodiment

The second embodiment of the present invention will be described next.FIG. 14 is a flowchart showing the processing to be performed whenX-rays are sensed in sensing mode 3. Processing up to the execution ofsensing is the same as that in the first embodiment. In the secondembodiment as well, when an X-ray irradiation sensing unit 150determines that X-ray irradiation has been performed, and a computerdevice 400 becomes ready for obtaining an image, obtained imageinformation stored in an image storage unit 190 is transferred to thecomputer device 400 (steps S1401 to S1403). The computer device 400which has received the image information differs from that in the firstembodiment in that it automatically processes the image as an imageobtained by misshooting without storing or displaying it. Even if thecomputer device 400 discards the image, an X-ray detection apparatus 100can obtain an image without any artifact by the next imaging operationupon preparing for normal imaging by performing a refresh operation(steps S1404 and S1405).

In addition, when performing misshooting processing, the computer device400 may record information, as its reason, which indicates that theimage has been obtained at an improper irradiation timing. At the sametime, a display device 410 may display a dialog indicating thatirradiation has been performed at an improper timing. The computerdevice 400 can properly manage the exposure dose for a patient bylinking information such as patient information and imaging conditionsto image information subjected to misshooting processing. In addition,the computer device 400 can also use the image as a diagnosis image bycanceling the misshooting processing. Subsequently, the computer device400 maintains a re-imaging enabled state with respect to the nextimaging operation based on the same conditions as those for the imageprocessed as the image obtained by misshooting. In contrast to this, ifthe X-ray detection apparatus 100 determines that no X-ray irradiationhas been performed, the apparatus immediately returns to sensing mode 3(preparatory irradiation determination period) and stands by withouttransferring any image (step S1406).

As described above, according to this embodiment, automaticallyprocessing an image as image obtained by misshooting can reduce the loadon the operator and quickly prepare for the next imaging operation. Thiscan improve the workflow.

Other Embodiments

According to other embodiments, a two-dimensional image sensing elementusing a PIN photoelectric conversion element may be used. In this case,it is not necessary to use a refresh power source as a power source fora voltage Vr, and initial reading in a preparation period is startedwithout refresh after actual reading in FIG. 9. Irradiation startsensing in sensing mode 1 is started a certain time after the start ofinitial reading. According to the above embodiments, a current flowingin the bias power source is I/V-converted to sense the start of X-rayirradiation. However, this is not exhaustive, and an X-ray irradiationsensor for the start of irradiation other than a two-dimensional imagesensing element 120 may be arranged on the X-ray incident surface sideof the X-ray sensor including the two-dimensional image sensing element120 and the scintillator to sense the irradiation of X-rays entering theX-ray sensor. The X-ray irradiation sensor is connected to a drivingunit (driving circuit) 165 to transmit a signal to the driving unit 165in accordance with the start of irradiation, thereby driving thetwo-dimensional image sensing element 120.

Embodiment(s) of the present invention can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

1-20. (canceled)
 21. A radiation detection apparatus comprising: aplurality of pixels for obtaining X-ray radiation image data based oncharges corresponding to X-ray radiation irradiated from a radiationgenerator through radiation imaging; a controller configured to performcontrols for the radiation imaging to the plurality of pixels; and asensing circuit configured to execute sensing whether or not theradiation irradiation to the plurality of pixels has been started bycomparing at least one of information which is obtained from theplurality of pixels and obtained separately from the X-ray radiationimage and information which is obtained from a X-ray radiation sensingsensor provided separately from the plurality of pixels, with athreshold, wherein the sensing circuit executes the sensing whilechanging sensing sensitivity of the sensor by changing the threshold, ina period during which the controller performs controls for the radiationimaging for obtaining X-ray radiation image data, and wherein thecontroller accumulates the charges on the plurality of pixels inaccordance with the sensing.
 22. The apparatus according to claim 21,further comprising a communication circuit configured to, in response totransmitting a control signal from a controller that controls theradiation detection apparatus, receive the control signal from thecontroller, wherein when an instruction to finish an examinationincluding at least one radiation imaging operation for a specific objectis input to the controller, the sensing circuit sets the sensingsensitivity lower in accordance with reception of a control signaloutput by the communication circuit from the controller in accordancewith an end of the examination.
 23. The apparatus according to claim 21,further comprising a communication circuit configured to, in response totransmitting a control signal from a controller that controls theradiation detection apparatus, receive the control signal from thecontroller, wherein when no specific object as a radiation imagingtarget is designated with respect to the controller, the sensing circuitsets the sensing sensitivity lower in accordance with reception of acontrol signal output from the controller.
 24. The apparatus accordingclaim 21, further comprising a communication circuit configured to, inresponse to transmitting a control signal from a controller thatcontrols the radiation detection apparatus, receive the control signalfrom the controller, wherein when no instruction signal to permitimaging for an examination is received from the controller for apredetermined period, the sensing circuit sets the sensing sensitivitylower in accordance with reception of a control signal output from thecontroller in accordance with an end of the examination.
 25. A method ofcontrolling a radiation detection apparatus having a plurality of pixelsfor obtaining X-ray radiation image data based on charges correspondingto X-ray radiation irradiated from a radiation generator throughradiation imaging, a controller configured to perform controls for theradiation imaging to the plurality of pixels, and a sensing circuitconfigured to execute sensing whether or not the radiation irradiationto the plurality of pixels has been started, based on at least one ofinformation which is obtained from the plurality of pixels and obtainedseparately from the X-ray radiation image and information which isobtained from a X-ray radiation sensing sensor provided separately fromthe plurality of pixels, the method comprising: executing, by thesensing circuit, the sensing while changing sensing sensitivity of thesensor so that the sensing sensitivity in a first period, in a periodduring which the controller performs controls for the radiation imagingfor obtaining X-ray radiation image data, is higher than the sensingsensitivity in a second period, in the period during which thecontroller performs controls for the radiation imaging for obtaining theX-ray radiation image data, having a lower probability of the radiationirradiation than the first period; and accumulating, by the controller,the charges on the plurality of pixels in accordance with the sensing.26. A non-transitory computer-readable storage medium storing a programfor causing a computer to execute a method of controlling a radiationdetection apparatus having a plurality of pixels for obtaining X-rayradiation image data based on charges corresponding to X-ray radiationirradiated from a radiation generator through radiation imaging; acontroller configured to perform controls for the radiation imaging tothe plurality of pixels, and a sensing circuit configured to executesensing whether or not the radiation irradiation to the plurality ofpixels has been started, based on at least one of information which isobtained from the plurality of pixels and obtained separately from theX-ray radiation image and information which is obtained from a X-rayradiation sensing sensor provided separately from the plurality ofpixels, the method comprising: executing, by the sensing circuit, thesensing while changing sensing sensitivity of the sensor so that thesensing sensitivity in a first period, in a period during which thecontroller performs controls for the radiation imaging for obtainingX-ray radiation image data, is higher than the sensing sensitivity in asecond period, in the period during which the controller performscontrols for the radiation imaging for obtaining the X-ray radiationimage data, having a lower probability of the radiation irradiation thanthe first period; and accumulating, by the controller, the charges onthe plurality of pixels in accordance with the sensing.